mrmint69

I just got a brand new fuel pressure gauge and hooked it up and ran it up to the windshield and used the wiper to hold it down. I took it out for a drive and it was 38 at idle and 44 with the vacuum line discounted. When i tap the throttle a little it goes from 38 to around 45 and the more gas i give it the higher it goes. It almost looks like an rpm gauge as it rises quickly with any throttle. At wot it goes up quickly to 48-49 and stays there so the volume is there. Are these normal readings?

Injuneer

They are for a boosted engine. The stock specs are:

-41-47psi at idle with no vacuum line (43.5 is the pressure the fuel injectors are flow rated at)

-connect the vacuum line and the pressure drops proportional to intake manifold vacuum, typically 6-8psi with a stock cam.

-at WTO/max load/max RPM without a blower fuel pressure will be close to, but slightly less than the pressure measured at idle, without the vacuum line.

Because you have a blower, your intake manifold is under increasing pressure (not vacuum) as the RPM's go up. Once you go into boost, the fuel pressure will start to rise, and at WOT/max load/max RPM, the fuel pressure will be the idle "no vacuum pressure" + the boost.

Your readings look completely normal.

mrmint69

I assumed the fuel pressure would stay around the same pressure at lower rpm's so it seems wierd for it to go up 6 psi with only tapping the gas and jumping the rpm's from 850 to 1200. The specs appear right but i don't remember my old gauge swinging up and down so much.

Injuneer

When you open the throttle, vacuum disappears. Since vacuum is pulling the rail pressure down from 44psi to 38psi, when you open the throttle and vacuum is greatly reduced, the pressure will jump up. The needle should be moving every time you move the throttle.